Lactones of mercapto carboxylic acids and process of preparing them



Patented June 25, 1946 ACIDS AND PROCESS THEM WllbnrA. Laaier, NewCastle County,

Kn 8M0, W du Pont de Norman PREPARING Delta-ignorant].

a Company, Wilmington,

DeL, a corporation of Delaware No Dram. Application September 19, SerialNo. 357,416

2: Claims. (cl. 260-321) This invention relates to mercapto carbotylicacids and derivatives thereof and a process for their preparation.

Frequently, organic compounds containing two different functional groupsin one molecule have especially useful applications. For example,compounds of this type have become of great industrial importance forthe preparation of polymeric materials. It is frequently desirable thatof the functional groups present in a compound at least one be areactive group, such as a carboxyl group, so that the molecule can beattached to another compound or material so that the properties of theremaining functional groups can be imparted to the material so treated.Heterofunctional organic compounds containing both a mercapto and acarboxyl group are of considerable utility but so far as we are aware nocommercially practical and general method for obtaining materials ofthis type has hitherto been available.

This invention has as its object an economical process for obtainingmercapto carboxylic acids and derivatives thereof. Another object is thepreparation of certain new and useful compounds. Other objects will beapparent from the following descriptionof the invention.

To accomplish these objects, an organic compound having at least onecarboxyl group or derivative thereof and a thiocarbonyl group or itssulfhydrate is catalytically hydrogenated. Alter- .natively, an organiccompound containing at least one carboxyl group and a carbonyl group orderivative thereof is catalytically hydrogenated in the presence ofhydrogen sulfide.

In practicing this invention the carbonyl group in a carbonyl carboxyliccompound may be converted to the thiocarbonyl group and hydrogenated ina single operation. The carbonyl carboxylic compound is charged into ahydrogenation autoclave together with sulfur as a source of hydrogensulfide and a sulfactive hydrogenation catalyst. 'The autoclave is thenfllled with hydrogen at superatmospherlc pressure and agitated andheated to a temperature at which reaction proceeds at a suitable rate,usually in the neighborhood of 150 C.. After the reaction is complete,as evidenced by no further hydrogen absorption, the autoclave is cooledand the product is filtered from the catalyst and blown with inert gasto drive out the unreacted hydrogen sulfide. The product may then beisolated or purified by the usual methods of distillation,crystallization or solvent extraction. The following examples show ingreater detail the practice of this invention in several of itsmodifications. The

amounts of materials referred to are parts by weight. Example I Asulfactive hydrogenation catalyst is prepared as follows: A solution of240 parts of sodium sulilde nonahydrate and 64 parts of sulfur in 1500parts of water is added with stirring to a solution of 238 parts ofcobalt chloride hexahydrate in 1700 parts of water. The blackprecipitate is mtered with suction and washed substantially free fromsoluble salts with water. Since the catalyst oxidizes spontaneously withresulting loss in catalytic activity when exposed to air, it is storedand used as an aqueous paste or, alternatively, the precipitate, afterwashing with water, is washed with an organic solvent such as dioxane toremove most of the water and stored and used as a non-aqueous paste.This catalyst is used to hydrogenate a ketocarboxyilc acid to amercaptocarboxylic acid as follows.

One hundred parts of commercial laevulinic acid, 60 parts of sulfur, and15 parts of cobalt polysulflde catalyst idry basis) prepared asdescribed above are charged into a hydrogenation autoclave fitted sothat the contents may be agitated. Hydrogen is then charged into theautoclave to a pressure of 1000 lbs/sq. in. and the autoclave is heatedto a temperature of 150 C. After the initial rapid reaction hassubsided, as evidenced by the decrease in the rate of hydrogenabsorption, the temperature is raised to 175' C. for four hours tocomplete the reaction. After cooling the autoclave, the contents areilltered to remove the catalyst and blown with nitrogen to remove theunreacted hydrogen suliide. Titration of an aliquot of the reactionmlxture with standard iodine solution indicates the presence of thiolequivalent to 37 parts of i-mercaptovaleric acid. The reaction mixtureis then iractionally distilled. There is obtained 67 parts of a fractionboiling at 94 to 95 C./22 mm. and 18 parts of a fraction boiling atC./22 min. The lower boiling fraction contains 25.5% of total sulfur and2.5% of thiol sulfur. has a density of di lmla and refractive index of n=l.4936. This material consists principally of the lactone of4-mercaptovalerlc acid formed by cyclization of the 4-mercaptovalericacid. The higher boiling fraction contains 22.3% of total sulfur and 14%of thiol sulfur. This material contains 59% of 'l-mercaptovaleric acidand the thiolactone into which it readily cyclicizes. The amount ofthiol obtained in the distilled fraction is less than that presentv.perature of 180 C. for 5 hours.v

asoaeao catalyst (C3) catalyst HaC=B(CH )gCO OH-l-H; -v CHtCI IBH (CHshCO OH trample II.

One hundred parts of commercialethyl acetoacetate and 35 parts of g ahydrogenation autoclave togetherwithxd parts of cobalt polysulfide paredas described in Example I, and 55 parts of ethanol solvent. Theautoclave is heated to 150 C. under an initial hydrogen pressure of 1000lbs/sq. in. Rapid reaction ensues as evidenced by the decrease inpressure and additional hydrogen ls added from time to time to maintainthe total pressure within the range from 1000 to 2000 lbs. per sq. in.After 3.5 hours heating no further hydrogen is absorbed and theautoclave is cooled, the products rinsed out with ethanol, and filteredfrom the catalyst. Excess hydrogen sulfide is removed by blowing thesolution with nitrogen, and the reaction mixture is distilled, thefollowing fractions being obtained: A foreshot of propanethiol-2 andethanol solvent is followed by a fraction boiling from 95 to 100 C./50mm. This fraction, obtained in the amount of 30 parts, analyzes for 87%purity as ethyl 3mercaptobutyrate. Water is formed in the course of thereaction, which hydrolyzes a part of the ethyl .acetoacetate to acetone.The latter compound is converted to propanethiol-Z. This side reactionmay be avoided largely by operating in the following manner. a

Ethyl acetoacetate is converted into, the corresponding ethylthioacetoacetajte bypassing streams of anhydrous hydrogen chloride andhydrogen sulfide through -asolut ionoi the' ester C; untilno' furtherhyin absolute alcohol at drogen sulfide 'rfeac 32, 4945 (1938). The

{iii- Mina, Chem.v Abst.

washed with water and finallyQdried over anhydrous sodiumsulfate. Thered-colored crude ethyl thioacetoacetate is then hydrogenatedin ethanolsolution using cobalt polysulfide catalyst; exactly as described in thepreceding paragraph omitted. On working obtained substantially exceptthat the sulfur is up the product there is pure ethyl B-mercaptobutyratein high yield.

Example III A nickel sulfide hydrogenation catalyst is prepared asdescribed in Example I for the cobalt sulfide catalyst except that anequivalent amount of nickel chloride hexahydrate is substituted for thecobalt chloride hexahydrate. Forty-seven parts of2-carbethoxycyclopentanone and 20 parts of sulfur are charged into ahydrogenation autoclave with 5 parts of nickel polysulfide catalyst and50 parts of dioxane solvent. The autoclave is filled with hydrogen to apressure of 810 to a tem- At the end of of hydrogen is lbs/sq. in. andagitated and heated this time no further absorption sulfur are I chargedinto catalyst (dry basis) preu eproduct is then di-- d with Water d h-loll layer separated and apparent and the autoclave is cooled and thecontents filtered to separate the catalyst and warmed under reducedpressure to remove the ,excess hydrogen sulfide and dioxane solvent. 5The residue is'a colorless, oily liquid consisting of a mixture of2-carbethoxycyclopentanethiol and cyclopentanethiol. The formation ofthe lay-product cyclopentanethiol may be avoided by hydrogenating thepreformed thioketo ester following tlie procedure described in thesecond paragraph Example II.

Example IV Forty parts bi -carbomethoxyvaleric aldehyde. 20 parts ofsulfur, and 5 parts of cobalt polysulfide catalyst prepared as describedin Example I are charged into an autoclave with 60 parts of methanolsolvent. The autoclave is filled with hydrogen to an initial pressure of800 lbs/sq. in. and heated during 45 minutes to 160 C. The reactioncommences at about 100 C. as evidenced by the decrease in pressure andis very rapid at 160 C. After 2.5 hoursheating no further pressure dropis observed and the autoclave is cooled and the contents filtered toseparate the catalyst and blown with nitrogen to remove the hydrogensulfide. Titration of an aliquot of the product indicates the conversionto 5-carbomethoxypentanethiol-l to be 48% of the theoretical.

reaction mixture under reduced pressure yields the colorless oily5-carbomethoxypentanethiol-1 which gives a yellow precipitate with leadacetate solution.

Example V Another type of sulfactive catalyst is prepared as follows:Finely divided pared by the sodium naphthalene reduction of anhydrouscobalt chloride) is suspended in methanol and treated at roomtemperature with a stream of hydrogen sulfide until the evolution ofhydrogen has ceased. The catalyst is then washedby decantation withmethanol until the excess hydrogen sulfide has been removed. Thecatalyst isstored and used as a methanol paste. Forty-twoipa'rtsOIo-ketohendecane-I, ll-dioic acid, 32 parts ot'suliur, 100 parts ofdioxane, and 10 parts of cobalt sulfide catalyst prepared as describedabove are charged into a hydrogenation autoclave together with hydrogenat an initial pressure of 1000 lbs/sq. in. The autoclave is agitated andheated at a temperature of 180 C. ior three hours... During this timethe reaction I ,y isJveryTrapid, as evidenced by the decrease'inhoursiat 1757 0. to insure action 'I'he'contents of the autoclave arefiltered-to separate the catalyst and blown with nitrogen to remove theexcess hydrogen sulfide. Iodine titration of an aliquotof the reactionmixture indicates the conversion to S-mercaptohendecane-l, ll-dioic acidto be 82% of the theo retical. The crude reaction mixture is warmedunder reduced pressure to remove the solvent and water present, leavingthe mercapto acid as a viscous liquid residue.

7 Example VI One hundred twenty-five parts of 4-keto-pimelic acid, 45parts of sulfur, and 15 parts of cobalt polysulfide catalyst prepared asdescribed in Example I are charged into an autoclave, together withhydrogen at an initial pressure of Removal of the methanol solvent bywarming the I pyrophoric cobalt (prepressure. Additional hydrogen isadded to main;

tain thetotalfpressure above 1000 lbs/sq. in. The

autoclave isfthen heated for an additional tw completion of the re- 80%conversion of 1000 lbs./sq. in. The autoclave is agitated and heated ata temperature of 100 to 1'70 C.ior five hours. During this time thetotal decrease in ressure amounts to 2400 lbs./sq. in. and more hydrogenis added as needed to keep the pressure within the range from 1000 to2000 lbs./sq. in. After filtering the contents oi the autoclave toseparate the catalyst, the crude reaction mixture is blown with nitrogento remove the excess hydrogen sulfide. Iodine titration of an aliquotoi! the reaction mixture indicates the presence oi a small amount ofi-mercaptopimelic acid. -Distillatlon oi the crude reaction mixtureyields an oily traction boiling at 190 to 200 C./4 mm.

The distillate is dissolved in a mixture oi benacne and ligroin and oncooling there is obtained,

absorption oihydrogen and it is necessary to add hydrogen irom time totime to maintain the toin the form oi white crystals, the pure lactoneoi s-mercaptopimellc acid. The compound melts at 59 to 61 C. Analysis ofthis material ll as 101- lows: Found: S=l8.50%; mol. wt. (bysaponification number)=l'73.9. Calculated: 8--l8.4l%: moi. wt.=1'74.1.The product of the hydrogenation reaction, i-mercaptopimelic acid, isunstable and readily cyclicizes to the lactone, as was the case withi-mercaptovaleric acid described in an earlier example. Thesetransformations may be formulated as follows:

eat. HOOC(CHs)|CB(CH|) CO0H B o BOOCKEH MCHBIUCINICOOK Example VIIForty-tour, parts of the saltoi 4- keto-pimelic acid, parts of sulfur.and 0 parts of cobalt polvsulfide catalyst prepared as describedinExample I are charged into a hydrovstoooionoioo cmitoooat t a; m.

tal pressure above 700 lbs/sq. in. Alter three hours no furtherabsorption of hydrogen is noted and after four hours the autoclave iscooled and the contents filtered irom the catalyst and blown 4 withnitrogen to remove the hydrogen sulfide. Titration of, an aliquot of thesolution indicates the presence oi diethyl 4-mercaptopimelate. in anamount corresponding to 22% conversion 0! the hate ester. Ondistillation there is obtained as the principal traction an oily liquidboiling at 142 to ME 0J2 mm. It 'is the ethyl ester of the lactone imercaptopimelic acid which is formed msrcapt ester. by cyclization withgiethanolg; These transformations beiormulated aslollows:

sioootonmcnsmcniiloooat 11.0

i IE$00C(0HI)ICH(CBI)ICO EtOli The above experiment is repeated undersimilar conditions except that an iron sulfide catalyst is substitutedfor the cobalt sulfide catalyst and the hydrogenation is carried out at175 C. The catalyst is prepared as iollows: A finely ground alloyconsisting of equal weights of iron and aluminumis treatedwith boilingaqueous sodium hydroxide solution to. remove the aluminum. The resultingfinely dividediroh powder is washed free from salts and alkali bydecantation and then washed free "from water with ethanol and asevidenced by the rapid decrease in pressure. 1

and additional hydrogen is added from time to time to maintain the totalpressure within the range of 1400 to 2000 lbs./sq. in. The autoclave isheated for a total time of 4 hours to insure completion or the reaction.The contents of the autoclave are then filtered to remove the catalystand blown with nitrogen to remove the excess hydrogen sulfide. Iodinetitration of a sample of the acidified aqueous solution indicates thepresence of the disodium salt 0! d-mercaptopimelic acid in anamountjoorresponding to the keto acid salt. On acidification, the freed-mercaptopimelic acid sepastored and used as an ethanol paste. Thisfinely divided pyrophoric iron is charged into the hydrogenationautoclavetogether with the other reactants. During the period of heatingthe autoclave up to reaction temperature the pyrophoric iron reacts withthe sulfur, forming an active iron sulfide hydrogenation catalyst. Aitercompletion of the reaction the product is worked up as described above.and the ethyl ester of the lactone oi i-mercaptopimelic v acidisobtained in high yield. v

The conversion or 'aldehydo=and ketocarboxylic compounds to thecorresponding mercapto-carboxylic compounds has been illustrated ratesout of the solution as an oil. This material is unstable and cyciicizeson distillation to the lactone of i-mercaptopimelic acid described inthepreceding example.

Example vm One hundred fifteen parts of diethyl i-ketopimelate, 32 partsof sulfur, and 10 parts of cobalt sulfide catalyst are charged into ahydrogenation autoclave. The autoclave is filled with hydrogen to aninitial pressure oi. 700 lbs/sq. in. and agitated and heated at atemperature oi 150 C. for four hours. The course of the reaction isfollowed by the decrease in pressure indicating in the foregoingexamples. 'Thisdnvention is, however, not limited to these particularcompounds and is likewise applicable generally to other compounds havingan aldehydo 0r keto group and a carboxyl group. As additional examplesof compounds that may be processed according to this invention, theremay be mentioned the tree acids, or the alkyl or aryl esters, amides,

alkyl or aryl substituted amides, and the anhydrides oi the followingcarbonyl carboxylic compounds: aldehydo acids such as glyoxylic acid;5-carboxyvaleric aldehyde, simple keto acids such as pyruvic acid,acetoacetic acid (ethyl acetoacetate, acetoacetamide,acetoacetyl-o-toluide, diacetoacetyl ethylene diamlde), 2-alkylor-arylacetoacetic acids, laevullnlc acid, acetopyruvic acid, ketostearicacids (4-ketostearic acid, lO-ketostearic acid, l2-k'etostearicacid,12-ketostearamide, ketostearin), benzoylacetic acid,betabenzoylpropionic acid, o-benzoylbenzoic acid; compounds having morethan one carboxylic group, as for example, mesoxalic acid, acetonedicarboxylic acid, acetosuccinic acid, and ketohendecanedioic acid. Inaddition to the foregoing classes of compounds, the carbonylcarboxyliccompounds may contain other functional groups in addition to thecarbonyl and carboxyl groups. Examples of such functional groups are theethylenic bond, the acetylenic bond, hydroxyl, amino, ether, halogen andnitro groups. Examples of compounds of this class are hydroxy keto acidssuch as Z-ketogluconic acid, unsaturated keto acids such abeta-benzoylacrylie acid, 11- canic acid, and a compound containing anether linkage. e hyl iuroyl cetate.

Certain carbonyl compounds readily form hydrates which are considered tohave the groupi s a on \tnil Such hydrates will behave as true carbonylgroups in the process of this invention and their conversion to thiolsis likewise a part of this invention. Generally, derivatives that arehydrolyzable to carbonyl compounds may also be converted to thecorresponding thiols by this process. Examples of compounds of thisclass are the hemiacetals, aldimines, ketimines, hydrazones,semicarbazones and anils of carbonyl carboxylic compounds.

The normal product obtained by the hydrogenation of a carbonylcarboxylic acid or derivative in the presence of hydrogen sulfideaccording to the process of this invention is the correspondingmercaptocarboxylic compound in which the mercapto group is attached tothe carbon atom originally forming the carbonyl group. As explained insome of the foregoing examples, however, when the carbonyl group is inthe four or five position with respect to the carboxyl group, theresuiting mercapto carboxylic compound may undergo cyclization with theformation of a lactone. Although not essential in most cases, solventsmay be employed in carrying out the hydrogenation process. Examples ofsolvents that may be used are water and organic solvents such ashydrocarbons, alcohols, ethers, and the like. If the free mercapto acidis desired, then it is preferable to use as the solvent water,hydrocarbons, or ethers. On the other hand, if the mercapto carboxylicester is desired, then it is preferable to use as .a solvent the alcoholcorresponding to the ester desired. When tli'eprocess is applied to betaaldehydoor ketocarboxylic compounds, it is preferable to use anhydroussolvents to minimize hydrolytic cleavage of the starting material. Inaddition to simple solvents, the reaction may also be accomplished inthe presence of such materials as alkalies, acids, ammonia, and amines.The use of acids in the reaction media frequently leads to more rapidconversion to thiols. The use of aqueous alkali as the solvent isdesirable for the conversion of deltaand gamma-carbonyl carboxyliccompounds to the corresponding thiols as this prevents the formation ofthiolactones. By carrying out the reaction in the presence of ammonia orprimary or secondary amines, mercapto carboxylic amides may be obtained.

In the foregoing examples, the use of sulfur as a source of hydrogensulfide has been illustrated, as this is an especially convenient way togenerate the desired reagent. However, hydrogen sulfide itself may becharged into the autoclave together with the other reactants; Instead ofhydrogen sulfide or sulfur, other sulfur compounds that are converted tohydrogen sulfide under the reaction conditions can be used. Ex-

amples of such materials are sulfur dioxide, ethyl tetrasulfide, carbonbisulfideand alkali or ammonium sulfides. The proportion of hydrogensulfide to carbonyl compound employed may be varied considerably.However, it is usually preferred to employ an excess of hydrogen sulfideor source of hydrogen sulfide over the amount theoretically required.

The process. of this invention may be operated over a considerable rangeof temperatures and pressures. Reaction occurs in many cases attemperatures as low as C., but usually at a low rate. As the temperatureis raised, the rate of reaction increases, and it is thereforepreferable to operate at temperatures above 100 C. The upper temperaturelimit at which the may be operated is determined by the thermalstability of the compound processed. In most cases, the compounds arestable at temperatures up to at least 200' C. and therefore it issuitable to operate at temperatures between 100 and 200 C. The reactionproceeds well, even at low pressures of hydrogen, but in order to insurea practicable rate of reaction it is desirable to operate at a hydrogenpressure of at least 100 lbs/sq. in. The upper, limit depends upon themechanical limitations of the equipment used for carrying out thereaction. a

As examples of sulfactive catalysts that may be used in carrying out theprocess of this invention, it has been found that certain metal sulfidesare especially suitable for this; purpose since these found tobeexceptionally active. Such catalysts may be prepared by ayarlety ofmethods, as, for example, by precipitating the metal sulfide from asolution of a metal salt with hydrogen sulfide, a solution of alkali oralkaline earth metal sulfide or polysulfide. or with ammonium I sulfideor polysulfide. Another. method that has been found to yield very activehydrogenation catalysts is to treat or activated metal suspended in aliquid medium with hydrogen sulfide or sulfur until sulfidation issubstantially complete. Other methods for obtaining metal sulfidecatalysts include heating powdered metals or metal compounds such as theoxides, carbonates, or sulfides with volatile sulfiding agents such assulfur, hydrogen sulfide, or carbon bisulfide.

The hydrogenating activity of the metal sulfides may be increasedfrequently-by treatment with hydrogen at elevated temperatures. Thehydrogen treatment of the metal sulfide in many cases can be combinedconveniently into a single operation with the hydrogenation reaction forwhich the catalyst is to be used.

Instead of charging the metal sulfide as such, it may be formed in situby placing the finely divided pyrophoric or activated metal in theautoclave together with the other reactants. The sulfur or hydrogensulfide present will convert the metal to the active metal sulfide inthe early stages of the reaction process. The catalyst employed may besubstantiall a pure metal sulfide or a combination of metal sulfides.Other substances may be present also, as for example,

kieselguhr, alumina, magnesia, carbon, and other supporting or promotermaterials.

process the finely divided pyrophoric By the term fsuliactivehydrogenation cata- "asusedhereinandintheclaims.wemeana catalys preparedas described in U. 8. Patents N0. 2.221.804 and 2.230.390. and which isactive for the catalytic hydroaenation oi the sulfur in organicmultisulfides, organic sulfur compounds having carbon-to-suliurunsaturation. and organic sulfur compounds havingsulfur-tomuneaturation.

The prop rtion of suliactive hydroaenation Q catalyst employed in theprocess of this invention maybe varied considerably. Depending upon theparticular cataiystused and the other conditions oi operation an amountof catalystoi'irom 0.5 tofic'b and usually from 2 to 10% or the weightor carbon carbonyl compound processed may be required to eflect reactionat a convenient rate.

As described in most of the foregoing exam plea. it is especiallyconvenient to form the thiccarbonyl compound and hydrogenate it to thecorresponding thiol in a single operation. However. it is considered tobe within the scope oi this invention to react a carbonyl carboxyliccompound with hydrosen sulfide by any suitable means and subsequently tohydro enate the reaction product with a sultactive hydro enationcatalyst to obtain the mercaptocarboxylic compound. A standard methodfor forming thiccarbonyl comp u ds compound in absolute alcohol andsimultaneously to pass streams of anhydrous hydro en chloride andhydrosen suliide through the cooled solution until no more hydrogensulfide is absorbed. Thereafter the alcohol. hydrogen chloride, andexcess hydrogen sulilde may be removed and the crude reaction producthydro enated'to the thiol. Other means of forming thiocarbonyl compoundsma be used. as for example. by reaction oi the a carbon l com ound withphosphorus pentesuliide. 'l'he thiocarbonyl com ounds in many casesreact with hydmcen sulilde to form sulihydrates-compounds havinathegrouping m hydrogenating the preformed thiocarbonyl compound or otherreaction product of carbonyl comp und with hydrpaen sulnde to thecorresponding thiol. the conditions employed are the same as thosedescribed for the combined formotion and hydro enation of thethiocarbonyl compound except that the presence of hydrosen sulfide isnot essential 'l'hioaldehydnand thioketocarboxyl pounds that may behydroaenated according to this invention are those corres onding to eachof the carbonyl compounds mentioned above, and their sulfhvdrates andpolvrners.

This invention constitutes a useful and eoonomical process forpreps-line mcrcapto carbonyllc compounds. These products are useful asintermediates for the preparation of polymers, dyestuffs. rubberchemicals and insecticides. For

example. the mercaoio carboxvlic acids may be oxidised to dibasicsuli'onic carboxylic acids which are useful chemical intermediates.

It is apparent that many widelydii'i'orent-embodiments 01' thisinvention may be made without departing from the spirit and scopethereoi and is to dissolve the carbonyl com-' polysulfide obtained as aprecipitate by reacting therefore it is not intended to be limitedexcept V as indicated in the appended claims.

We claim:

1. 'Iheprocessiorthe comprises reacting ot a suliactive hydroaenationand substances which with hydro en yield hydrogen sulfide attemperatures above 100' C. v

3. The rocess for the preparation of mercapto carboxylic compouruh whichcomprisesreacting a thiocarbonyl carbmlic acid substance with hydrogenin the presence of a suliactive hydrogenation catalyst.

reactinfl ing of the add. its anhydride. its esters and its amides withhydrogen and a substance selected irom the group consisting oi hydrogensulfide andsubstances which with hydrogen yield hydrogen sulfide attemperatures above 100' C.

rocess ior the prep ration oi mercapto carbotylic compounds whichcomprises reoi the acid. its anhydride, its esters and its'amides withhydrosen and a substance selected from the group consisting 0! hydrogensulfide and substances which with hydrogen yield hydroflen sulfide attemperatures the class co the preparat on of mercapto carbosyliccompounds which comprises recarbOXY ic acid substance selectedconsisting of the acid. its hydride, its esters and its amides withhydrogen and a substance selected. from the group consistina or hydrosensulfide and substances which with hydrogen yield hydroaen sulfide attemtures above 100 C.. in the presence oi a metal a soluble iron groupmetal salt with a substance selected from the group consisting of alkalisultides and polysuifides, alkaline earth sulfides, and ammonium sulfideand polysuli'ide.

'l. The process for the preparation of mercapto carboxylic compoundswhich comprises reacting a carbonyl carboxylic acid substance selectedfrom the class consisting of the acid. its anhydrlde, its esters and itsamides with hydrogen and a substance selected from the group consistingof hydrogen sulfide and substances which with yield hydrogen sulfide attemperatures above 100' (7., in the presence of a metal sulfide obtainedby treating a nnely divided active metal with a sulfiding agent selectedfrom the group comprising sulfur, hydrogen sulfide, and carbonbisulfide. p I

8. The process for the preparation of mercanto carboxylic compoundswhich comprises reacting a carbonyl carboxyllc acid substance selectedfrom the class consisting oi the acid. its anhydrido, its esters and itsamides with hydrogen and a substance selected from the groupconsistpreparation 0! meme-pil 75 ing of hydrogen sulfide and substanceswhich for the-preparation oi mercapto ,atures above 100' C.

carboxylic compounds which comprises reacting in the presence of asuli'active hydrogenation cataiyst an aldehydo'carhoxylic acid substancesel'ected from the class consisting of the acid, its anhydride, itsesters, and its amides,-with hydrogen and a substance selected from thesroup con-.

- sisting of hydrogen sulfide and substances which with hydrogen yieldhydrogen sulfide at temper- 10. The process in accordance with claim 9characterised in that the aldehydo caiboay'iic acid substance is anomega-aldehyde carboxylic acid substance.

11. The process in characterised in that accordance claim 9 the aldehydocarboxyiic acid substance is an omeza-oarbomcthomaleric aldehyde.

12. The process for the preparation of mercapto carhoxylic compoundswhich comprises reactin: in the presence 01 a sulfactlve hydrogenationcatalyst at ketocarboxylic acid substance selected from the classconsisting of the acid, its anhydride, its esters, and its amides, withhydrogen and a substance selected from the sroup consist- 1 'ing or hyosen with hydrogen yield sulfide and substances which hydrogen sulfideat temperatures above 100' C. i

13. The process in accordance with claim 12 characterised in that theketocarboxylic acid substance is a ketoinonocarboxylic acid.

14. The process in accordance with claim 12id'lhepmcessinlccordmcewithclaimilharacterizedinthatthehctocerbonlicacidsubstance is d-ketopimelic acid.

17. The process for the reparation oi mercapto carbowlic compounds whichcomprises reactinginthepreseneeodasuliactivehydmenation catalyst athiocarbonyl carboxylic acid subnance selected from the class consistingoi the acid, its anhydride, its esters, and its amides, withhydrogenandasubstanceselectedi'romthezroupconsistin or hydrogen sulfideand substances which with hy sen yield hydrosensulfide at temperaturesabove 100' 18. The process in accordance with claim 17 characterized inthat the thi acid substance is acid substance is a thioketocarboxyiicacid.

20. The process for the preparation of marcapto carboxylic compoundswhich comprises reacting, in the presence or molybdenum sulfide, a

i-memaptopimelic acid.

22. Asancw chemicai ompoundanaiiphatie mercapto-dicarboniic mercaptogroup is separated from atleast one of the cart-Julio crows by at leastthreecarbon characterized in that the ketocarboxylic acid sub-' as atomsin contia'uom relati n.

stance is 12-ketostearic acid.

15. The process in accordance with claim 12 characterisedinthat theketocarboxylieacidsub licacidsubstance.

23. As a litgwmchsmicaimmpound the lactone o amercap carboxy compound, I

- WILBURALAZIER.

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compozmdinwhichtbe'

